Synthesis of p-Nitro-stilbene Derivatives with Different Linking Bonds:An Attempt to Tune Spectroscopy of Dyes with Molecular Engineering

The synthesis, characterization and spectroscopy of a range of novel substituted p‐nitro‐stilbene derivatives with different bridging bonds were presented. The molecular structure characterization was carried out with ¹H NMR, ¹³C NMR and elemental analysis. The ultraviolet/visible spectroscopy and photoluminescence of the compounds were investigated in various solvents. The maximal absorption wavelength of the nitro‐stilbene derivatives with an ether bond exhibited approximate 30 to 40 nm bathochromic shift compared to that of nitro‐stilbene dyes with an ester bond. Furthermore, the nitro‐stilbene derivatives with an ether bond displayed obvious photoluminescence, while the nitro‐stilbene derivatives with an ester bond showed weak fluorescence emission. The detection of the cyclic voltammograms of the nitro‐stilbene derivatives showed that the nitro‐stilbene compounds with different linking bonds exhibited different redox proceses at various scan rates. The theroretical calculations of HOMO and LUMO energy of nitro‐stilbene derivatives showed that the energy gaps between HOMO and LUMO of 3 and 4 were lower than those of 1 and 2 . The electron density of the frontier orbitals of nitro‐stilbene derivatives was observed to be affacted by the linking bonds, which thus made it possible to tune the spectroscopy of these dyes with chemical strategy. The differential scanning calorimetry and thermogravimetry showed that the thermal stabilities of these dyes were not much affected by the linking bond. The results presented in this paper would be great interest in development of ideal nitro‐stilbene derivatives for special purposes.     

Synthesis,spectral characterization,DFT studies and biological activity of novel Ligand 1‐(2‐cyclohexyl thioethyl) piperidine and its complexes with group 12 metal chlorides

C₆H₁₁S^‐Na⁺ (generated insitu by reaction of NaOH with C₆H₁₁SH) on treatment with 1‐(2‐chloroethyl) piperidine hydrochloride under N₂ atmosphere resulted in (1‐(2‐cyclohexyl thioethyl) piperidine) ( L ¹ ) as orange solid. It's complexes having the formula [ZnCl₂. L¹] ( 1 ), [CdCl₂. (L¹)] ( 2 ) and [HgCl₂. L¹] ( 3 ) have been prepared. L ¹ and its complexes 1‐3 were characterized on the basis of physico‐chemical and spectral (FT‐IR, Mass, ¹H, ¹³C and DEPT 135^o NMR) studies. Powder XRD diffraction pattern reveals the crystalline nature of L¹ and complex 1 . Complexes 1‐3 adopt distorted tetrahedral geometry showing bidentate mode of coordination through S and N. Using DFT‐based optimization of structures, the HOMO‐LUMO energy gaps and molecular electrostatic potential maps (EPM) of compound L¹ and complexes 1‐ 3 were theoretically calculated at the B3LYP/6‐311G (d, p) level of theory. HOMO‐LUMO energy gap was calculated which allowed the calculation of relative properties like chemical hardness, chemical inertness, chemical potential, nucleophilicity and electrophillicity index of the synthesized products. The experimentally obtained IR and NMR results showed a good correlation with those of the theoretical ones. Ligand L ¹ and complexes 1‐3 display significant antibacterial and antifungal activity.     

Highly Pure Synthesis,Spectral Assignments,and Two‐Photon Properties of Cruciform Porphyrin Pentamers Fused with Benzene Units

Tetrameric porphyrin formation of 2‐hydroxymethylpyrrole fused with porphyrins through a bicyclo[2.2.2]octadiene unit gave bicyclo[2.2.2]octadiene‐fused porphyrin pentamers. Thermal conversion of the pentamers gave fully π‐conjugated cruciform porphyrin pentamers fused with benzene units in quantitative yields. UV/Vis spectra of fully π‐conjugated porphyrin pentamers showed one very strong Q absorption and were quite different from those of usual porphyrins. From TD‐DFT calculations, the HOMO level is 0.49 eV higher than the HOMO?1 level. The LUMO and LUMO+1 levels are very close and are lower by more than 0.27 eV than those of other unoccupied MOs. The strong Q absorption was interpreted as two mutually orthogonal single‐electron transitions (683 nm: 86 %, HOMO→LUMO; 680 nm: 86 %, HOMO→LUMO+1). The two‐photon absorption (TPA) cross section value (σ⁽²⁾) of the benzene‐fused porphyrin pentamer was estimated to be 3900 GM at 1500 nm, which is strongly correlated with a cruciform molecular structure with multidirectional π‐conjugation pathways.     

The Pi‐Nature of Methyl Obtained by the Natural Bond Orbital Method: Orbital‐Based Rationalizations of Site‐Dependent Substitution Effects on Fine Color‐Tuning of Luminescence

Both C‐H bonding and antibonding (σ_CH and σ*_CH) of a methyl group would contribute to the highest occupied or lowest unoccupied molecular orbitals (HOMO or LUMO) in methylated derivatives of Ir(ppz)₂ 3 iq (ppz = 1‐phenylpyrazole and 3iq = isoquinoline‐3‐carboxylate). This is found by analysis of HOMO (or LUMO) formed by linear combination of bond orbitals using the natural bond orbital (NBO) method. The elevated level of HOMO (or LUMO) uniformly found for each methylated derivative, indicating the σ_CH‐destabilization outweighs the σ*_CH‐stabilization. To broaden the HOMO‐LUMO gap, methylation at a carbon having smaller contribution to HOMO and/or larger contribution to LUMO is suggested.     

Synthesis and Characterization of Multinanometer‐Sized Expanded Dendralenes with an iso‐Poly(triacetylene) Backbone

A series of [n]dendralenes (n =3, 4, 8, 3b – d (Fig. 1)) expanded with buta‐1,3‐diynediyl moieties between the CC bonds were prepared by repetitive acetylenic scaffolding of 3‐(cyclohexylidene)penta‐1,4‐diyne building blocks (Scheme). These remarkably unstable iso‐poly(triacetylene) (iso‐PTA) oligomers were characterized by ¹H‐ and ¹³C NMR (Fig. 3 and Table 1), IR, and UV/VIS (Figs. 4 and 6 and Table 2) spectroscopy, as well as mass spectrometry (Fig. 2). The expanded [8]dendralene contains 40 C(sp)‐ and C(sp²)‐atoms in the backbone and represents the longest iso‐PTA oligomer prepared to date. HOMO‐LUMO Gap energies were determined as a function of oligomeric length (Fig. 5 and Table 3), providing insight into the degree of π‐electron delocalization in these cross‐conjugated chromophores. A continous drop in the HOMO‐LUMO gap with increasing number of monomeric repeating units provides evidence that cross‐conjugation along the oligomeric backbone is effective to some extent. The limiting HOMO‐LUMO gap energy for an infinitely long, buta‐1,3‐diynediyl‐expanded dendralene was extrapolated to about 3.3–3.5 eV. The conformational preferences of the expanded dendralenes were analyzed in semi‐empirical calculations, revealing energetic preferences for planar or slightly twisted s‐cis and ‘U‐shaped' geometries.     

Theoretical Investigations on the Electronic and Optical Properties of Luminescent Poly（alkylthiophene-co-pyridine）

Quantum-chemical techniques were applied to investigate a series of conjugated polymers： poly（3-octylthien-2,5-ylene-co-pyrid-2,6-ylene） （pl）, poly[pyrid-2,6-ylenebis（3-octylthien-2,5-ylene）] （p2） and poly[pyrid-2,5-ylenebis（3-octylthien-2,5-ylene）] （p3） comprising alternating n-excessive 3-alkylthiophene and n-deficient meta- or para-linked pyridine moieties. Their ground state and excited state structures were optimized with density functional theory B3LYP method, and the optical properties were calculated by the time-dependent density functional theory （TD-DFT） and ZINDO/S methods. Their HOMO-LUMO gaps （An-L）, the lowest excitation energies （Eex）, ionization potentials （IP） and electron affinities （EA） were obtained by extrapolating those of the polymers to the inverse chain length equal to zero （1/n=0）. The calculated results showed that the decrease of pyridylene content increased the HOMO level and decreased the LUMO level while the para-linkage further contributed to it. The IP are in the order： p1〉p2〉p3 but EA are： p1〈p2〈p3. In addition, the decrease of the pyridylene content and the para-linked pyridylene in the backbone of the polythiophene resulted in a narrowed energy gap and bathochromic absorption and emission peaks.     

Investigations on regio‐ and stereoselectivities in cycloadditions involving α‐ (3‐pyridyl)‐N‐phenylnitrone: Development of an efficient route to novel nicotine analogs

Thermal reactions of hitherto α‐(3‐pyridyl)‐N‐phenylnitrone ( 1 ) with mono‐substituted electron‐rich and electron‐neutral dipolarophiles are regio‐, and stereo‐selective (exo‐selective), controlled by LUMO ‐ dipole ‐ HOMO‐ dipolarophile interaction, and furnish syn‐5‐substituted‐3‐(3‐pyridyl)‐isoxazolidines ( 5 ) in high yields. With electron deficient dipolarophiles such as acrylonitrile there is observed a loss of regioselectivity as well as stereoselectivity and the regioselectivity is reversed in reactions with methyl vinyl ketone and methyl acrylate, due to intervention of HOMO‐dipole ‐ LUMO‐dipolarophile interaction, affording 4‐substi‐tuted‐3‐(3‐pyridyl)‐isoxazolidines ( 7 ) as major products. Reactions of nitrone ( 1 ) with disubstituted dipolarophiles such as methyl methacrylate and ethyl coronate furnish methyl syn‐5‐methy‐3‐pyridyl‐1‐phenyl‐isoxazolidine‐5‐carboxylate ( 8 ) and ethyl anti‐5‐methy‐3‐pyridyl‐1‐phenyl‐isoxazolidine‐4‐carboxylate ( 10 ), respectively, in high yields. Reaction with N‐Phenylmaleimide affords novel isoxazolidino‐pyrro‐lidinediones bearing a 3‐pyridyl moiety ( 11, 12 ). A mechanistic rationalization of the obtained results in terms of electronic, steric and secondary interactions is proffered.     

Experimental verification of diverging mechanisms in the binding of ether,thioether, and sulfone ligands to a dirhodium tetracarboxylate

Complexation of the oxygen atom in 2‐butylphenylethers and sulfur in 2‐butylphenylthioethers to a rhodium atom in dirhodium tetracarboxylate Rh^(II)₂[(R)‐(+)‐MTPA]₄ is compared. Oxygen atoms complex via electrostatic attraction exclusively leading to an increase in α effects on C‐2 complexation shifts in the sequence OCH₃ > F > Br > NO₂. However, that trend is opposite in thioethers. This can be rationalized by an additional highest occupied molecular orbital (HOMO)–LUMO interaction and the response of this interaction upon complex formation shifts. Thereby, an experimental evidence was found for the existence of the HOMO–LUMO binding mechanism which has been proposed previously based on theoretical considerations and indirect spectroscopic evidence. Sulfones hardly bind to Rh^(II)₂[(R)‐(+)‐MTPA]₄. Diastereomeric dispersion effects at ¹³C and ¹H signals can be observed for all compounds indicating that enantiodifferentiation is easy in all classes of functionalities. Copyright © 2010 John Wiley & Sons, Ltd.     

The regioselectivity in the reactions of N-aryl-C-ethoxycarbonylnitrilimines with acrylic acid derivatives

The cycloaddition of a series of C-ethoxycarbonyl-N-arylnitrilimines 5a-f to acrylic acid derivatives namely acrylamide, acrylonitrile and ethyl acrylate has been studied. Under thermal conditions 1,3-dipolar cycloadditions proceed with complete regioselectivity to give 5-R substituted 2-pyrazolines 8–10 in high yield. The structures of the cycloadducts 8–10 were confirmed by ¹³C nmr, ¹H nmr and ir spectra. The regioselectivity is interpreted in terms of HOMO(nitrilimine)-LUMO(dipolarophile) interaction.     

Photophysical properties of the isomorphic emissive RNA nucleobase analogues and effect of water solution,ribose, and base pairing: A theoretical study

In the present work, a comprehensive theoretical investigation on the excited state properties of the isomorphic emissive RNA nucleobase analogues, namely ^tzA, ^tzG, ^tzC, and ^tzU, was performed. Vertical transition energies are determined with the time‐dependent density functional theory method at both the B3LYP and CAM‐B3LYP levels using the 6‐311++G(d,p) basis set. The nature of the low‐lying singlet excited states is discussed and the results are compared with the findings from experiment and those for thieno analogues and natural bases. In gas phase, it was found that the S₁ state is ππ* in nature for all the tz‐bases except for ^tzA, for which the S₁ state is predicted to be nπ* in nature with the ππ* state being the S₂. While in water solution, the S₁ state for all tz‐bases are predicted to be ππ* dominated by the configuration HOMO→LUMO. Compared with natural bases, the lowest ππ* states are about 0.85–1.22 eV red‐shifted. When compared with thieno analogues, it is interesting to note that the S₁ state (ππ*) transition energies of the two counterparts from the two alphabets are nearly equal due to the very little differences of their HOMO‐LUMO gaps. In addition, it was found that the hydration + PCM model can perfectly reproduce the photophysical properties of the tz‐bases since the calculated excitation maxima and fluorescence are in good agreement with the experimental data. The microenvironment effects of linking to ribose, base pairing, and further hydration of base pairs were also studied.     

Investigation of spectroscopic studies and DFT calculations on glucofuranose derivatives of dithiophosphonates

Abstract

2,4-Bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide (Lawesson’s reagent: LR) was reacted with 1,2:5,6-di-O-cyclohexylidene-α-D-glucofuranose and 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose in toluene and gave rise to crude dithiophosphonic acids. The crude dithiophosphonic acids were treated with excess triethylamine and the triethylammonium salts of dithiophosphonic acids (1) and (2) were isolated by crystallization method. Compounds 1 and 2 were characterized by elemental analysis, IR, and NMR (¹H-, ¹³C- and ³¹P-) spectroscopies and mass spectrometry. In addition, NMR spectra, the electronic properties (the electronic chemical potential, electronegativity, chemical hardness and the global electrophilicity index) and NBO analysis of compound 2 have been calculated by using the Gaussian 16?W program. The electronic properties were calculated using Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energies by density functional method (DFT/B3LYP) at 6-31G(d,p) level. The HOMO and LUMO energies are ?5.9 and ?0.72?eV, respectively. The HOMO–LUMO energy difference is 5.18?eV and this value shows that compound 2 has a high stability and low reactivity.     

A Semiempirical Study of Carbon Nanotubes with Finite Tubular Length and Various Tubular Diameters

A semiempirical PM3 quantum computational method has been used to generate the electronic and optimized geometrical structure of SWNT of zigzag and armchair types. We shed light on the electronic structures of SWNT with various diameters and lengths of the tube. Particularly, the calculated HOMO, LUMO and band‐gap of SWNT are not monotonic but exhibit a well‐defined oscillation, which depends on the tubular diameter and the tubular length. Calculated HOMO, LUMO and band‐gap of the zigzag SWNTs have oscillated with tubular diameter as they contain an odd or even number of benzenoids in the circular plane of the carbon nanotube. The zigzag SWNTs with an odd number of benzenoids have a higher band‐gap than those of SWNTs with an even number of benzenoids in the circular plane of the carbon nanotube. Calculated results also reveal that the tubular length in the zigzag SWNTs influences the band‐gaps very little. For the armchair SWNT, calculated HOMO, LUMO and band‐gap contained the oscillate depending on the number of carbon sections in the tubular length axis. Their repeat sections are 3n‐1, 3n and 3n+1. The armchair SWNT with 3n+1 sections has a high band‐gap while the SWNTs with 3n‐1 sections have a low band‐gap. The tubular diameters of armchair SWNT influence the HOMO, LUMO and band gap very little.     

Synthesis,molecular conformation,vibrational, electronic transition,and chemical shift assignments of 4-(thiophene-3-ylmethoxy)phthalonitrile: a combined experimental and theoretical analysis

This work presents the synthesis and characterization of a novel compound, 4-(thiophene-3-ylmethoxy)phthalonitrile (TMP). The spectroscopic properties of the compound were examined by FT-IR, FT-Raman, NMR, and UV techniques. FT-IR and FT-Raman spectra in solid state were observed in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The ¹H and ¹³C NMR spectra were recorded in CDCl₃ solution. The UV absorption spectrum of the compound that dissolved in THF was recorded in the range of 200–800 nm. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts (¹³C NMR and ¹H NMR) were calculated using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The HOMO and LUMO analyses have been used to elucidate information regarding charge transfer within the molecule. Comparison of the calculated frequencies, NMR chemical shifts, absorption wavelengths with the experimental values revealed that DFT method produces good results.     

2‐Bromo‐6‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)pyridine,a new unexpected bifunctional building block for combinatorial chemistry

The first reported structure of a pyridin‐2‐ylboron derivative, viz. the title compound, C₁₁H₁₅BBrNO₂, (I), is compared with its regioisomer 2‐bromo‐5‐(4,4,5,5‐tetra­methyl‐1,3,2‐dioxa­borolan‐2‐yl)­pyridine, (II) [Sopková‐de Oliveira Santos, Lancelot, Bouillon & Rault (2003). Acta Cryst. C59, o111o113 ]. Structural differences are observed, firstly in the orientation of the dioxaborolane ring with respect to the pyridine ring and secondly in the bond angles of the BO₂ group. These differences do not explain the experimentally observed differences in chemical reactivity between (I) and (II) but do confirm the relatively lower stability of (I). However, ab initio calculations of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), based on the known crystal structures of the two compounds, show different distributions, which correspond to the differences observed during chemical reactions.     

Colorless to Purple–Red Switching Electrochromic Anthraquinone Imides with Broad Visible/Near‐IR Absorptions in the Radical Anion State: Simulation‐Aided Molecular Design

The large redshift of near‐infrared (NIR) absorptions of nitro‐substituted anthraquinone imide (Nitro‐AQI) radical anions, relative to other AQI derivatives, is rationalized based on quantum chemical calculations. Calculations reveal that the delocalization effects of electronegative substitution in the radical anion states is dramatically enhanced, thus leading to a significant decrease in the HOMO–LUMO band gap in the radical anion states. Based on this understanding, an AQI derivative with an even stronger electron‐withdrawing dicyanovinyl (di‐CN) substituent was designed and prepared. The resulting molecule, di‐CN‐AQI, displays no absorption in the Vis/NIR region in the neutral state, but absorbs intensively in the range of λ=700–1000 (λ_max≈860 nm) and λ=1100–1800 nm (λ_max≈1400 nm) upon one‐electron reduction; this is accompanied by a transition from a highly transmissive colorless solution to one that is purple–red. The relationship between calculated radical anionic HOMO–LUMO gaps and the electron‐withdrawing capacity of the substituents is also determined by employing Hammett parameter, which could serve as a theoretical tool for further molecular design.     

Syntheses,Spectroscopic and DFT Studies of Two New D‐π‐A Compounds

Two novel 1,3‐dithiole‐2‐ylidene derivatives with a push–pull structures, 3‐(4,5‐dicarbomethoxy‐1,3‐dithiol‐2‐ylidene)naphthopyranone 1 and 3‐(4,5‐dimethylthio‐1,3‐dithiol‐2‐ylidene)naphthopyranone 2 , have been synthesized and characterized by ¹H NMR, IR, MS. The UV–vis spectra of 1 , 2 in CH₂Cl₂, the lowest‐energy absorption bands, are centered at 280, 316, and 430 nm for 1 and 284, 317, and 450 nm for 2 , respectively, which are caused by the HOMO → LUMO single electron promotion. Furthermore, the steady‐state fluorescence originating states of 1 , 2 from the excited charge‐transfer were observed. To estimate the position and energies of frontier orbitals for 1 , 2 , DFT calculations were performed using the Gaussian 03 program at the B3LYP/6‐31 G* level. The calculated vertical excitation energies are in good agreement with the experimental data. The high HOMO–LUMO gaps of 1 (3.08 eV) and 2 (3.00 eV) indicate high kinetic stability of the title compounds.     

The Effect of Substituents on the Fluorescent Properties of Para‐Phenylenevinylene

Semi‐empirical AM1 method and density function theory were used to study the electronic structures and spectroscopic characteristics of the luminescent material analogous to PPV (para‐phenylenevinylene) oligomers attached to different substituents. It was indicated that the LUMO‐HOMO energy gaps were changed distinctly by means of the electron‐donating effect, conjugated effect and steric effect. The fluorescent wavelength in the fluorescent spectrum, the main absorption peaks in the electronic spectra and the chief bands in the IR spectra for the complexes were red‐shifted, relative to those of the parent molecule, owing to the extension of the conjugated system, the shrink of the energy gap and the weakening of the C=C bonds, respectively. The ¹³C chemical shifts were also moved obviously when the substituents on the matrix were changed.     

4‐(3,5‐Dimethyl‐1H‐pyrazol‐4‐ylmethyl)‐3,5‐dimethyl‐1H‐pyrazol‐2‐ium dihydrogen phosphate: a combined X‐ray and DFT study

The molecular structure of the title salt, C₁₁H₁₇N₄⁺·H₂PO₄⁻, has been determined from single‐crystal X‐ray analysis and compared with the structure calculated by density functional theory (DFT) at the BLYP level. The crystal packing in the title compound is stabilized primarily by intermolecular N—H...O, O—H...N and O—H...O hydrogen bonds and π–π stacking interactions, and thus a three‐dimensional supramolecular honeycomb network consisting of R₄²(10), R₄⁴(14) and R₄⁴(24) ring motifs is established. The HOMO–LUMO energy gap (1.338 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital) indicates a high chemical reactivity for the title compound.     

Tuning of the electronic properties of H‐passivated armchair graphene nanoribbons by mild border oxidation: Theoretical study on periodic models

We report the results of a DFT study of the electronic properties, intended as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, of periodic models of H‐passivated armchair graphene nanoribbons (a‐GNRs) as that synthetized by bottom‐up technique, functionalized by vicinal dialdehydic groups. This material can be obtained by border oxidation in mild and easy to control conditions with ¹Δ_g O₂ as we reported in our previous paper (Ghigo et al., ChemPhysChem 2015, 16, 3030). The calculations show that the two models of border oxidized a‐GNRs (model A, 0.98 nm and model B, 1.35 nm wide) present LUMO and HOMO energies lowered by an extend roughly linearly dependent on the amount of oxygen chemically bound. The frontier orbital energy variations dependence on the % wt of oxygen bound are, for model A: ?0.12 eV for the LUMO and ?0.05 eV for the HOMO; for model B: ?0.15 eV (HOMO) and ?0.06 eV (LUMO). © 2016 Wiley Periodicals, Inc.